Effects of feeding canola screenings on apparent digestibility, growth performance and carcass characteristics of feedlot lambs

Abstract

Commercial coarse canola screenings (CS) were substituted for barley grain, and the resulting experimental diets (0, 20, 45, 70 and 95% CS, as-fed) were evaluated in feedlot lambs, while the 0, 45 and 95% CS diets were evaluated in a digestibility study using Romanov × Suffolk lambs. The CS comprised 60% canola (as whole, broken and immature seeds), 25% weed seeds and 15% chaff/dust. The control diet (0% CS) contained 75% barley and 20% alfalfa (as a protein/fibre source). Dietary crude protein (CP) increased with inclusion of CS and was lowest for control and 20% CS diets (13%) and highest for the 95% CS diet (14.4%). Digestibilities of dry matter (DM), organic matter (OM), neutral detergent fibre (NDF) and acid detergent fibre (ADF) were reduced (P < 0.05) in the 95% diet as compared with the control diet. Nitrogen retention by lambs was three times higher in the control group than in the 95% CS group (P < 0.001). Growth and feed conversion efficiency in feedlot lambs were linearly reduced (P < 0.001) with increasing dietary CS, but so was saturation of carcass fat (P < 0.001), which may benefit human health. Reduced lamb performance with CS was likely related to its high contents of crude fat (9%, DM basis) and ash (14%, DM basis). Valuing CS at 86% of the cost of barley, incorporation of up to 45% CS in feeder lamb diets would be cost effective. Key words: Canola, by-product, screenings, lamb, growth, carcass